Recovery of hydrogen fluoride in an alkylation process



Patented Apr. 2.7, 1948 RECOVERY OF HYDROGEN FLUORID IN AN ALKYLATION PROCESS I Roy E. Vinyard, Borger, Tex.,

assignor to Phillips Petroleum Company, a corporation of Delaware Application July 18, 1944, Serial No. 545.415

The present invention relates to a process for l the alkylation of hydrocarbons by the use of hydrogen fluoride or hydrofluoric acid and similar reagents as alkylation catalysts and relates particularly to a process for the recovery of hydrogen fluoride and removal therefrom of acid-soluble hydrocarbon oils which are formed in such alkylation reactions.

Processes for the alkylation of hydrocarbons, for example, alkylation of isobutane with ethylene to produce diisopropyl and alkylation of isobutane with butylene to produce isooctanes, by means of catalysts such as hydrofluoric acid are well known to the art. Such processes are described, for example, in Frey Patents No. 2,322,800 and 2,317,901 and also in the articles by Frey in Chemical and Metallurgical Engineering, 1943, vol. 50, pages 126 to 128 (November, 1943), and Philnews, December, 1943, pages 7 to 10. In such processes, a mixture of an alkylatable substance, such as isobutane,l and an alkylating reactant, such as 1- butene or 2butene or a butane-butene fraction, are agitated together Iwith liquid concentrated hydrofluoric acid or liquid anhydrous hydrogen fluoride at a temperature within the range of ap- 2 Claims. (Cl. 260683.4)

proximately to approximately 100 F. The

mixture is then allowed to settle and the hydrocarbon layer is separated from the acid layer. The acid layer is recycled to the reactor or contactor to catalyze the alkylation' of further amounts of alkylatable substance.

The hydrocarbon layer. which still contains some hydrogen fluoride or concentrated hydrofluoric acid, is then subjected to distillation, whereby an azeotrope is `formed between the lower-boiling or unalkylated hydrocarbons and the hydrouoric acid. which are recycled to the contactor, generally after allowing the condensed distillate to stratify and separating the two layers. After the hydrouoric acid has 4been expelled from the hydrocarbon layer in this manner, the hydrocarbon layer is then treated to effect the removal of any small proportions of alkyl fluorides or other organic iluorine compounds which may have been formed in the reaction and the alkylated products are recovered in more or less conventional manner.

rAs the hydrouoric acid continues to be reused in the process, acid-soluble oils begin to accumulate therein. These acid-soluble oilswhich are referred to in the copending application of Frederick E. Frey, Serial No. 429,961, filed February 7, 1942, and which are a by-product of the alkylation reaction, vary greatly in composition and characteristics but are in generalnormally liquid materials that are soluble in hydrogen fluoride, partly soluble in water and partially soluble in hydrocarbons. They appear to have a tendency to reduce the catalytic: activity of hydrouoric acid and to vary the course of the alkylation reaction. For these reasons, their removal from the hydroiluoric acid before lt is recycled -for reuse in alkylatlon processes -is generally necessary. The amount of these acid-soluble oils which is formed may amount to from 1 to 2 per cent or more of the alkylated product. A

'typical acid-soluble oil has the following characteristics: Specific gravity at 25 C 0.8881

Refractive index at 20 C--. 1.5013 Unsaturation '(cc. 1% bromine soin. per cc.) 34.9 Sulfur, per cent by wt 2.17 Fluorine, per cent by wt -v 0.0013 4Color Dark red to brown in transmitted light Solubility in 98% HzSO4 80% Anline point 35 C.

The sulfur in this acid-soluble oil probably originates for the most part from impurities present in the hydrocarbons treated and in smaller part from the hydrofluoric acid used in the particular .alkylation A method for recovery of hydrogen iluoride from this oil is described in said cepending application of Frederick E. Frey.

The present invention is moreparticularly directed to the process of recovering spent hydroiluo'ric acid and removing acid-soluble oils therefrom. v

It is an object of the present invention 'to pro'- vide in a continuous alkylation process a process for the recovery of hydrogen fluoride or hydroiluorc acid from alkylation reaction mixtures and effect the removal of acid-soluble oils therefrom. Y

It is a further object of the present invention to provi-de such a process ,in which the removal of acid-soluble oils from the hydrouorlc acid is effected without the introduction of other undesirable` materials into the reaction mixture.

Other objects and advantages of the invention, some of which are referred to specifically hereinafter, will be apparent to those skilled in the art.

In accordance with the process of the invention, acid-soluble oils are removed from the hydrogen fluoride or hydrofluoric acid layer containing light hydrocarbons that are separated from a hydrocarbon alkylation reaction mixture by a distillation procedure in which a heavy hydrocarbon altillatio y Y 3 kylate obtained as a b .-produc't in the process is used to absorb the light hydrocarbons and thereby reduce the pressure prevailing during the dis- The distillation and the subsequent separation of hydroiluoric acid and light hydrocarbons are thereby facilitated. The invention also contemplates a further improved procedure whereby the'light hydrocarbons are freed from the heavy hydrocarbon alkylate absorption oil introduced in this manner so that they may be returned to the alkylation reaction mixture without the heavy hydrocarbon alkylate.

A preferred embodiment of the process of my invention is representedy on the accompanying drawing, which is a flow diagram thereof. Inaccordance with this preferred embodiment, hydrocarbons to be subjected to alkylation and hydroiluoric acid are charged through conduit I to re actor 2. In this reactor the hydrocarbons, which may be a mixture of isobutane and ethylene, are mixed intimately with the hydroiluoric acid by means of stirrers for a suitable period of time. The mixture then flows through conduit 3 to acidsettling tank 4. v

In the acid-settling tank 4, the two layers are separated, the lower or acid layer being returned to the reactor through conduit 5 by means of pump 8 and conduit 'I, and the upper or hydrocarbon layer being passed through conduit 8 to feed tank 9. From the feed tank 9, the hydrocarbon layer, which contains entrained and dissolved hydrofluoric acid, is charged through conduit Ill by means of pump II to azeotrope tower I2.

Inthe azeotrope tower I2, which is a fractional-distillation apparatus, the entrained and dissolved hydrouoric acid is separated from the major portion of the accompanying hydrocarbon by means of distillation, the hydrofluoric acid forming an azeotropic mixture with'isobutane, which is generally used in excess when isobutane is alkylated with ethylene, oran azeotrope with another low-boiling hydrocarbon. This azeotrope is the overhead of the distillation and passes through conduit I3 and condenser I4 into settling tank I5. A separation of acid and hydrocarbon from the azeotropic mixture in settling tank I5 takes place and the hydrocarbon is returnedvto azeotrope tower I2 through conduit I6 by means of pump I'I. The acid which separates out in settling tank I5 is returned through conduit I8 by means of pump I9 through conduit 2i) into acid-settling tank 4, where itis commingled with the eiiiuent from reactor 2.. Instead of being returned to acid settling tank 4 it may be passed directly to reactor 2, if desired. This alternative isnot represented on the drawing. Part of the light hydrocarbons from settling tank I5, instead of being returned as reflux to azeotropetower I2, may be charged to reactor 2. The bottoms inthe azeotrope tower I2 consist of hydrocarbons which are referred to hereinafter as total hydrocarbon effluent. This total hydrocarbon eiiiuent is removed through outlet 2l and is subjected to a recovery treatment. The unreacted lower-boiling hydrocarbons are separated from the alkylate by fractional distillation, preferably after subjecting the total hydrocarbon eiliuent to deuorination by treatment' with .selective solvents or by passing the effluent over bauxite eiliuent and recovered. The heavy alkylate is used as hereinafter described; some of it may be removed from the process. v

Instead of making a separationv of acidand hydrocarbon in acid settling tank I5, the unseparated acid and hydrocarbon material'from azeotrope tower I2Ymay be returned directly to scid settler 4 or to reactor z. This alternative is not represented on the drawing. Normally the azeotrope tower I2 is maintained at a higher prevailing operating pressure than acid settler 4 or I settler 4, which may be heated to vaporization or other contact material, asdescribed, for example, in the application of Frederick E. Frey.

Serial No. 398,361., led June 16, 1941 (Patent. No. 2,347,945). The desired alkylatedhydrocarbon fraction is then separated from heavy .trainers 24 are provided. of the tower is packed with lump coal 25 or other v reactor 2. Advantage may be taken of these differences in pressure to`dispense with the pumps I1 and I3 and eliminate acid settling tank I5 by returning the unseparated acid and hydrocarbon material from azeotrope tower I2 directly to acid settler 4 or reactor 2, -in accordance with this alternative.

The acid in acid settler 4 will contain absorbed and dissolved acid-soluble oils. These acidsoluble oils, whose characteristics were referred `to hereinbefore, generally have a higher boiling -point than the heavy alkylate fraction, a lower API gravity, and are much more highly unsaturated than the alkylate fraction. Ii not removed, these acid-soluble oils accumulate in the'recycled acid and have a deleterious eiect on the alkylation reaction. Theseacid-soluble oils appear to lower the yield of alkylated product in the reaction, have an effect on the course of the allwlation reaction, since the resulting products generally have a lower octane number than is obtained by alkylation in the absence of acidsoluble oils, and they appear to favor the formation of organic iiuorine compoundsin thealkylate and further amounts of acid-soluble oils.

The removal of these acid-soluble oils from the acid is effected. in accordance with the preferred embodiment of my invention, as follows:

All or a portion of the acid layer from acid temperature or lower, is passed through conduit 5 by means of pump 5 through conduit 22 .into flash tower 23. This flash tower is a simple fractionating colinnn in which ballles or mistengranular material that is inert to hydrouoric acid. The acid-soluble oils collect in the packing 25 and are withdrawn periodically through outlet 26. The overhead distillate consists of hydrofluoric acid together with hydrocarbons such as isobutan having lower boiling points than the acid-soluble oils. The overhead leaving the flash' tower 23 through conduit 21 passes' into a bubble tower 28, which is a conventional fractionating tower having two or more plates or trays provided with bubble caps, that is also in communication with the tower 23 by return-now conduit 29, and then passes through conduit 30 and condenser 3|, condenser 32, conduit 33 and into accumulator 34'.

To reduce the vapor pressure in the system from the flash tower 23 to accumulator 34, heavy The bottom portion 1942, patented May 15, 1945,` Patent N0. 2,376,051.

The purpose and use of the heavy alkylate in the process as described `in said application are entirely different from`those of the present in-` vention. In the process of the present invention, the heavy alkylate or other hydrocarbon absorption oil is not contacted with acid-soluble oils or with materials containing substantial proportions of acid-soluble oils.

i In operating with accumulator 34 and separator 4|, which is the preferred method of practicing the process of thelnvention, the lower acid layer in accumulator 34 is maintained at a more or less constant level therein -by drawing oil the mixed hydrocarbon (heavy alkylate) and acid layer through conduit 39 by means of pump 40 into separator 4I. 'I'he pressure in accumulator 34 and in the connecting conduit 30 is controlled by means of the addition or injection of heavy alkylate through conduit 35 and by control of the liquid level in accumulator 34.

This liquid level may beautomatically regulated by a valve 45 on separator. 4I controlled by a liquid-level control 46. Alternatively the pressure in conduit 30 may be controlled and the process operated'in such manner that no sub- `and most advantageouslyl ushed with heavy alkylate itself. In atypical operation this heavy alkylate is charged tothe pump at the rate V`of 5 barrels per hour or more and is.commin gled with the acid and heavy alkylate passing through the pump and is removed in separator 4| together with the heavy alkylate in the other materials therein.

In this manner the amount of acid-soluble oils which are recycled to the reactor may be controlled. There is no deleterious effect produced on recycling small proportions of the heavy a1- kylate fraction back into the reactor, should any befretained in the acid circulating through conduits 42, 38 and 1; that which is returned to the acid settler 4 is separated therein and is passed forward with the total hydrocarbon efuent and maybe again recovered at the outlet 2| of azeotrope` tower I2. The heavy alkylate, in which are dissolved the light hydrocarbons i associated with the hydrouoric acid,` facilitates stantial vapor phase is present in accumulator 34 and the liquid level (mixed hydrocarbon and acid phase) or gas-vapor interface is permitted to be at some point in condensers 3| or 32. The

valve 45 may be, in such event, controlled automatically by an alternative pressure control 41 in convention-a1 manner. The pressure which it will generally be desirable to maintain in con- `duit 30 by either of these two or other alternative methods is between approximately 20 and approximately 50 pounds per square inch gage.

In theV separator 4I, the upper mixed'hydrocarbonand acid layer is drawn off, preferablyv automatically through valve 45 as described and conduit 43 into conduit 20, through which it is charged into acid settler 4.. The lower acid phase or layer in separator 4I is returned to the reactor 2 Vthrough conduits 42 and 38, or may be returned to bubble ,tower 28, as hereinafter disclosed.

The function of separator 4| is to separate acid from heavy alkylate. All of .the heavy alkylate in separator 4| together with all or a portion of the acid is returned through conduits 43 and 20 to acid settler 4. Acid free from heavy alkylate, which is to be used as reflux in bubble tower 28, is discharged at the bottom of separator 4| and ,is passed through conduits 42 and 44. Some of the acid removed from the bottom of separator 4| may be returned to reactor 2 through conduits 42, 38 and ,'I. The amount of acid charged back to reactor 2 in this manner may .be controlled-by a valve 50 which is actuated automatically by a liquid-level control 5|.

The various pumps are constructed of suitable acid-resisting materials and with packing glands that may .be flushedwith hydrocarbon or other material to reduce the possibility of leakage and corrosion. Pump 6 is flushed with isobutane which is charged from an external source through the gland packing. The gland packings of pumps I I and |'I may be flushediwith petroleum lubricating oil in a similar manner. How ever, the gland packing of pump 4|) is preferably the separation of the acid from light hydrocarbons in accumulator 34 and separator 4|. The light hydrocarbons remain dissolved in the heavy alkylate.

In a typical example of a method of practicing the invention, isobutane and ethylene together with hydrofiuoric acid are charged continuously to reactor 2. Theresulting alkylation reaction mixture is charged to acid settler 4I operating at a temperature of approximately 80 F. and the hydrocarbon layer is passed to feed tank 9 and distilled in azeotrope tower I2. The charge to the azeotrope tower I2 is at a rate of approximately 1000 barrels per hour; of this vapproximately barrels per hour pass over as overhead and approximately 900 barrelsper per hour and is subjected to distillation in flash which is operating at a temperature tower 23, of approximately 260 F. From the bottom of the ash tower 23, acid-soluble oils and water are removed at a rate of approximately 2 barrels per hour. The bubble tower 28 connected to the viiash tower 23 is operated at a temperature of aproximately F. and a pressurerof approxi'- mately 40 pounds per square inch, which is maintained by introduction of heavy alkylate the rate. of approximately 12 barrels per hour and by control of the liquid level in accumulator 34. About 5 barrels per hour of heavy alkylateis charged to pump 40 to flush the gland seals thereof. The temperature of accumulator 34 is approximately 80 F. The acid phase from separator 4| is returned to the bubble tower 28 at the rate of approximately 14 barrels per hour. The mixed acid and heavy alkylate phase from separator 4| :is charged back to the acid separator 4 at the rate of approximately 53 vbarrels per hour (217 barrels per hour of heavy alkylate introduced through conduit l35 and gland seals of pump 40 and 36 barrels per hour of hydrouoric acid andabsorbed butanes).

In other operations it is to be understood that these ilow rates and temperatures may be varied over a Wide range, dependent upc-n the type of hydrocarbon material being treated and the character of heavy alkylate and similar factors, The amount of. acid which is removed from circulation between the acid settler and the reactor will also be variable and' dependent upon the reaction conditions prevailing and the rate of iormationuor acid-soluble oils which acumulate in the recycle stream. In general it may be stated that the amount of heavy alkylate or other hydrocarbon absorption oil which is added isl such as to maintain a pressure oi approximately' 20 to approximately 50 pounds per square inch gage in the bubble tower A2l 'or conduit 30 of the system and thereby facilitate the distillation and subsequent separation of the acidand hydrocarbons inthe acidstream.

Instead of using heavy alkylate for the absorption of liquid hydrocarbons and to maintain the desired pressure. other hydrocarbon materials which have a low vapor pressure and are substantially inert with respect tothe light hydrocarbons in the presence ci hydroiluoric acid and which are capable of dissolvingthe light hydrocarbons may be used. Thus heavy normally liquid normal paramn hydrocarbons may be used.

Heavy alkylate is a preferredmaterial since it is readily available as a byproduct in such alkylation processes/and is substantially inert and not substantially susceptible to further reaction I under the prevailing conditions.

It is to be understood that the foregoing description is merely illustrative, that the draw-l in'g is merely a diagrammatic representation of the 110W of materials in the process, and that the actual apparatus which will be required may include heaters, pumps, valves (some of which .are represented), pressure gauges, iiow meters,

heat exchangers, reflux accumulators, surge Atanks and other conventional equipment which will be. understood by those skilled in the art to which the invention pertains.

It is' further contemplated that the apparatus v wiu be constructed of metals and other materials which are inert or resistant to hydrotluoric acid and/or other substances which are used in contact with the apparatus.V Such materials of f 8 zone at about 260 F. avvaporous overhead product comprising hydroiiuoric acid and light hydroca rbous and a liquid bottom product comprising acid-soluble oils, paing said overhead product to a second distillation zone operating at about 175 F., removing from said second distillation zone a liquid bottom product and passing same back to said ilrst -dlstilaltion zone as a reflux therefor, removing also from said second distil lation zone a vaporous overhead product comprising hydroiluoric acid and light hydrocarbons, separately contacting saidV latter vaporous overhead product from said vsecond distillation zone with a heavy alkylate obtained from thealkylation reaction to substantially absorb said light hydrocarbons, said heavy alkylate being introconstruction are described in the article by ji Charles M. Fehr, "Materialsjof construction for anhydrous hydroiluoric acid, in Chem. Met. Eng., 1943, vol. 50, page 129 (November, 1943), and in the articles of Frey referred to hereinbefore. f

Inasmuch as the foregoing description comprises preferred embodiments of the invention. it

is to be understood that the invention is not limited thereto and that alterations and modiiications may be made therein without departing from the scope of the invention or the scope of the appended claims.

I claim:

1. An improved continuous process for the alkylation of an alkylatable hydrocarbon with an olefin in the presence of concentrated hydroiluoric acid as an alkylation catalyst and for an improved recovery of said concentrated acid catalyst, which comprises continuously -passing an alkylatable hydrocarbon and an olefin hydrocar-V bon together with saidihydroiluoric acid to a reaction zone under alkylation conditions and subjecting them to reaction therein, passing the reaction mixture to an acid-settling zone and duced into'said latter vaporous overhead product in an amount such that the pressure of said overhead product` is about 40 pounds per square inch gage, thereafter cooling said latter vaporous overhead product and added heavy alkylate to condense remaining unabsorbed vapors andseparating arresulting liquid-acid phase comprising puried hydrouorlc acid from a resulting liquid alkylate phase comprising said heavy alkylate Y and absorbed iight hydrocarbons, passing a portion of said puried hydrofluoric acid to said second distillation zone as a reux therefor and passing another portion of said purified hydrofluoric acid to said reaction zone. controlling the ilow of said puried acid tosaid reaction zone responsive to the liquid level of said acid phase, passing said liquid alkylate phase to said acidsettling zone for subsequent recoveryv of said heavy alkylate in the fractionation of the hydrocarbon phase therefrom, and controlling the flow of said alkylate phase to the settling zone responsive to the pressure of said overhead product,

2. An improved continuous process for the alkylation 'of an alkylatable hydrocarbon with an olen in the presence of concentrated` hydroiluoric acid as an alkylation catalyst and for an improved recovery of said concentrated acid catalyst, which comprises Vcontinuously passing an alkylatable hydrocarbon and an olefin hydrocarbon together with said hydrouoric acid to a reaction zone under alkylation conditions and subjecting them to reaction therein, passing the reaction mixture to an acid-settling zone and therein separating a liquid hydrocarbon phase from a liquid hydroiluoric acid phase which contains light hydrocarbons and acid-soluble oils dissolved therein, separately fractionating said hydrocarbon phase to recover light alkylate and heavy alkylate and recirculating a portion of said acid phase together with fresh hydrocarbon reactants to said reaction zone, passing another portion of said acid phase to a distillation zone, flash distilling from said distillation zone at an elevated temperature a vaporous overhead product comprising hydrofiuoric acid and light hydrocarbons and a liquid bottom product comprising acid-soluble oils, separately contacting said vaporous overhead product from said distillation. zone with a heavy alkylate obtained from the alkylation reaction to substantially absorby said light hydrocarbons, said heavy alkylate being introduced into saltiV vaporous overhead product in an amount such that the pressure of said over-l head `product is between about 20 and about 50 pounds per square inch gage, thereafter cooling said vaporous overheadproduct and added heavy alkylate toI condense remaining unabsorbed va'- pors and separating a resulting liquid acid phase Y comprising` purified hydrofluoric acid from a ling the ow of said action zone responsive to the acid phase, passing said liquid alkylate phase ille of this patent:

resulting liquid alkylate phase comprising said heavy allwlate and absorbed light hydrocarbons, passing a portion of said purified hydrouoric acid to said distillationzone as a' reux therefor and passing another portion of said puriiied hydroriluoric acid to said reaction zone, control- -puritlm1 acid to said re'- `quid level ofvsaid to said acid-settling zone for subsequent recovery oi' said heavy alkylate in the fractionation o1' the hydrocarbon phase therefrom, and controlling the ilow of said alkylate phase to the settling zone responsive to the pressure oi.' said overhead product.

ROY E.,VIN`YARD.

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Engs, Pittsburgh, NOV. 14-16, 1943, and

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(Presented atAm. Inst. Y 

